There are many processes wherein articles, such as electronic devices, coatings, encapsulations or shaped articles have to be manufactured as multilayered bodies since the process requires to use, at first an adhesion layer or support material before the final coating is applied or the final article is completed. Examples of such processes are, in particular, printing, coating, encapsulation or other mounting processes. The encapsulation of solar cells in photovoltaic modules using silicones is e.g. possible by a one step process, but then the wafer-type semiconductor has to be fixed by any other means. If a two step process is applied i.e. the currently proposed materials have some disadvantages in terms of curing rates, transparency or additional process steps. It has been observed that if addition cured silicone rubbers are used in a first layer to adhere and fix e.g. a semiconductor or are used as a primer layer or a support for the next layer then such next layer does not adhere onto the cured first layer. Another requirement for such interfaces between the two layers is the resistance against some outstanding climate conditions and the need to adhere on many other substrates. Either only the first layer should adhere to such a substrate or both layers should adhere to a substrate in order to provide a multilayered adhesion body between two substrates. This requires on the one hand a good adhesion of the (in particular two) silicone layers to several substrates, i.e. glass, plastic layers such as, thermoplastic or duromeric films, sheets, boxes, metal conductors or semiconductors, such as wafer-type silicon cells, metals, ceramic, glass and also glass-fibre reinforced plastic, and on the other hand the silicone layers must have an excellent layer-to-layer adhesion, that is, the layers must not suffer form cohesive failure during the life-time of the articles comprising them.
Currently photovoltaic cells are generally encapsulated via a vacuum lamination process using ethylene-vinyl acetate (EVA) at approximately 150° C. instead of using silicone layers. Silicone encapsulants were the material of choice due to their insulating properties and their resistibility against extreme temperature changes and radiation for the early manufacture of photovoltaic modules, particularly for satellites and spacecraft. In mass production processes, when solar modules were beginning to be built for the terrestrial market, organic encapsulants like EVA replaced silicones. In recent years long-time durability and efficiency increase has became more important, so that again silicone with its UV radiation stability has become more preferred. In order to build modules with defined front and back layer upon semiconductors with defined thickness a two layer encapsulation process is necessary. The preferred silicone elastomer materials are addition curable or UV curable two-part silicone compositions. Within this kind of processes there is in particular a need for a process wherein a first silicone layer between glass superstrate and semiconductor cells is cured and in a second step a silicone layer is sealed while curing onto the first coated substrate to achieve a complete encapsulation of the semiconductor and parts of the metallic leads.
It is a general experience that not all silicone elastomers curable by a hydrosilylation reaction adhere to each other, when cured stepwise.
EP 431979 describes a silicone composite of an addition cured silicone gel which can be laminated with a vinylsiloxane polymer, which builds a fully flexible and secured gel layer. U.S. Pat. No. 4,889,576 specifies the connection between silicone-coated fabrics via a silicone rubber adhesive to produce big and seamless silicone coated fabrics. The patent discloses a process to build up silicone laminates via consecutive 2 step polyaddition reactions. U.S. Pat. No. 7,572,514 B2 describes in particular the application of silicone elastomers as multilayer coating for the protection or mechanical strengthening of various flexible substrates such as woven or non-woven fibrous substrates in relative thin thicknesses. The examples are silent about filler-containing compositions. While the feature of a surface density SD of the unreacted, residual alkenyl groups, per nm2 in the first layer appear to be essential, the method of determining such parameter does not appear to be clear at all. Moreover, while the patent describes that the ratio R of the SiH-groups to the Si-alkenyl-groups is defined to be ≦1 (corresponding to a Si-alkenyl excess) it appears that none of the examples satisfy such a feature, leaving doubt about the underlying invention. Furthermore in this respect the patent also does not describe the circumstances in the second layer leaving alone for a filler-containing layer. WO 2011107592 is related to PV-encapsulant compositions comprising silica fillers, which have excellent adhesive properties towards glass at long time damp-heat conditions. The description does not disclose adhesion of these silicones to each other after one of these compositions is already cured. EP 1644989 describes a 2-step process using an encapsulation process wherein first a semiconductor wafer is placed onto glass superstrate using an uncured silicone resin adhesive. After the curing step of the first adhesive layer a second encapsulant composition is uniformly applied to totally encapsulate the whole module by means of curtain coaters. WO 2011151430 describes a two-step encapsulation process for manufacturing solar modules using for example liquid or paste like silicone compositions. In this process a layer is applied on the glass superstrate which can be cured after both are rolled onto the semiconductor sheets and a second layer. The second layer which comprises the same material is coated over the semiconductor onto the opposite side of the semiconductor and parts of the first layer. U.S. Pat. No. 4,057,439 discloses an encapsulation process wherein a carrier tray is first coated with a two part addition curable silicone composition to build a layer, then is cured. In the next step the semiconductor sheets or wafers are encapsulated by a second silicone composition such as another two-part addition curable silicone which is more transparent establishing a thicker layer adhering to the first silicone layer having a high resistance against delamination. U.S. Pat. No. 4,322,261 describes a solar PV-encapsulant system, which has two silicone compositions selected from different or identical materials, whereby at least one of the two silicone materials is a heat vulcanizable EVC (Elastomères Vulcanisant à Chaud) material cured by peroxides at 110-180° C. WO2012041674 discloses a process for the manufacture of light cured silicone insulators, whereby a conventional primer is used and hardened in the presence of an UV-sensitive crosslinking catalyst which has been added in any desired sequence, i.e. before, during or after hardening of said silicone primer composition.